1. Field of the Invention
The present invention relates to a process for manufacturing a fiber keeping circular polarization and a device for implementing this process.
2. Description of the Prior Art
The monomode fibers usually manufactured for telecommunications always present a small amount of linear birefringence and circular birefringence. Consequently, these fibers keep neither linear polarization nor circular polariization.
It is possible to make the fiber very linear birefringent by breaking up the circular symmetry to the advantage of a planar symmetry.
It is also possible to consider a reverse method, which consists in introducing a high circular birefringence so as to keep the circular polarization.
One solution for creating this circular polarization consists in subjecting the glass fiber to a static twisting stress, for example applied externally by twisting between its two ends: one effect of twisting this fiber is to introduce a circular birefringence therein.
The present invention provides a process for keeping a twisted state in the fiber. It allows a fiber to be obtained with helical structure or chiralic structure. But this fiber may be of any section, it may thus have a complex geometry.
Any twisting stress creating a circular birefringence, a process of the prior art described in the European patent application published under the No. 0 078 733, consists in twisting a fiber which is already drawn out and maintaining it mechanically in this stress condition, by coating the fiber with a rigid envelope such as an additional glass layer.
The disadvantages of this process are:
on the one hand, fragilization of the fiber by introducing high stresses at the periphery of the fiber,
on the other hand, the need of external mechanical fixing means "maintaining" the twist.
The invention overcomes these disadvantages by envisaging a step for remelting the surface of the fiber carried out simultaneously with steps for drawing and twisting same.